Has PrE 7 ever worked on this computer?
Are you getting the error message (exact and full statement might be useful), when you attempt to launch PrE 7?
First, I would post the full specs. of your computer, and especially the video card/chip info, and the installed video driver. An obsolete video driver is the main cause (but not the only one) for Premiere Elements to not launch.
Next, I would see this FAQ Entry: http://forums.adobe.com/thread/792580?tstart=0
Could you right click the Premiere Elements 7 desktop icon, select Run As Administrator, and let us know if the problem is resolved.
I was going to suggest first a complete and clean/uninstall, but I had someone with similar problems do the uninstall/reinstall only to have the Run As Administrator as the fix.
If that does not work and you do go the uninstall and reinstall route, please consider....
You will probably want to try a complete and clean uninstall/reinstall of your Premiere Elements 7 to determine if that resolves the problem. If you have any user customer presets you may want to check out a thread that I wrote a while back on such considerations when uninstalling Premiere Elements 7.
If you have any questions on anything in the thread cited, please ask me here at the Adobe Forums.
I typically write problems with the same symptoms can (often do) have different causes, but the above turns out to be the remedy more often than not.
We will be watching for your results for all the questions.
Again, while there ARE times, where a full uninstall, clean and reinstall WILL fix some problems, I tend to keep that down my list, and look for other solutions first.
The Adobe Technical Support folk, in another part of the world, have that as "phase 1," on their scripts, and it usually is not necessary, though it CAN fix some things.
Not sure why you would recommend it as a first step, when there is much more info, that has not yet been provided?
Because it is a quick and a high % tool for remedy in this type of situation The results are either going to be immediate or provide excellent direction in any subsequent troubleshooting if necessary.